The answer depends on the type of twins: one or two sperm can be involved in conceiving twins.
Here's a breakdown:
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Identical (Monozygotic) Twins: One sperm fertilizes one egg, and this single fertilized egg then splits into two separate embryos. Therefore, only one sperm is involved. These twins share virtually identical DNA.
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Fraternal (Dizygotic) Twins: Two separate eggs are released from the ovaries during ovulation and are fertilized by two separate sperm. These twins are genetically no more similar than any other siblings, and can be of different sexes.
| Twin Type | Eggs Involved | Sperm Involved | Genetic Similarity |
|---|---|---|---|
| Identical (Monozygotic) | One | One | Virtually Identical |
| Fraternal (Dizygotic) | Two | Two | Like Siblings |
Therefore, while identical twins result from one sperm, fraternal twins are created by two sperm.
